Angiogenesis is a physiological process of tissue vascularization involving the growth of new blood vessels into a tissue wherever there is a need for them. For example, in a condition of oxygen deprivation as this might similarly be the case after wound formation, it is thought that cells release angiogenic factors thus inducing new vessel growth. For instance, vascular endothelial growth factor is perceived as the most important factor inducing proliferation of endothelial cells, the cells that form the vessels, leading to vascularization.
However, this physiological process might be deregulated in several pathological conditions, leading to an excessive and unnecessary or even harmful formation of new vessels, which is also referred to as neovascularization. On the one hand, this condition of neovascularization itself might cause a disease or pathological condition, e.g. in case of excessive scar formation or neovascular glaucoma. On the other hand, neovascularization promotes the progression of certain diseases as this is e.g. triggered by several solid solid tumors, e.g. breast cancer, prostate cancer or lymphomas like Hodgkin or non-Hodgkin lymphomas, or non-solid tumors like multiple myeloma.
Since angiogenesis or neovascularization is a hallmark of tumors, it is a concept in anti-cancer therapy to inhibit the formation of new vessels and thus to “starve” the tumor. Several new compounds have been developed aiming at blocking the proliferation and migration of endothelial cells. For instance, a monoclonal antibody against VEGF—bevacizumab (Avastin)—is successfully used in patients with various tumors to prevent metastasis and to shrink the tumors.
In addition to antibodies blocking VEGF and its receptor VEGFR small molecules are widely used as tyrosine-kinase-inhibitors (TKIs like Sunitinib and 2nd generation drugs Dovitinib=TKi 258) are summarized in reviews by Mukherji et al. or Heidegger et al. in the context of prostate cancer (Mukherji D, Temraz S, Wehbe D, Shamseddine A: Angiogenesis and anti-angiogenic therapy in prostate cancer. Critical Reviews in Oncology/Hematology 87 (2013) 122-131; Heidegger I, Massoner P, Eder I E, Pircher A, Pichler R, Aigner F, Bektic J, Horninger W, Klocker H: Novel therapeutic approaches for the treatment of castration-resistant prostate cancer. Journal of Steroid Biochemistry & Molecular Biology 138 (2013) 248-256).
However, the intake of bevacizumab or small molecule inhibitors may be accompanied with several serious and/or less serious side effects; moreover, development of drug resistance is regularly observed in the clinical setting during the course of the treatment. Hence, there is a need for novel target molecules for anti-angiogenic therapy, the therapy being associated with less side effects.
Recently, steroid hormones have been controversially evaluated for their effect on angiogenesis. For instance, Frank-Lissbrant and colleagues described the rapid neovascularization in rat ventral prostate lobe of castrated rats after repeated subcutaneous dosing of testosterone. (Franck-Lissbrant I, Häggström S, Damber J E, Bergh A: Testosterone stimulates angiogenesis and vascular regrowth in the ventral prostate in castrated adult rats. Endocrinology 1998; 139(2):451-6).
Further, Liao et al. described an effect of testosterone to promote vascular endothelial cell migration of cultured human umbilical endothelial cells (HUVECs) (Liao W, Huang W, Guo Y, Xin M, Fu X: Testosterone promotes vascular endothelial cell migration via upregulation of ROCK-2/moesin cascade. Mol Biol Rep (2013) 40:6729-6735).
A role of testosterone in regulating endothelial function and playing a role in the development and maturation of endothelial progenitor cells in the context of erectile physiology is further suggested in a review of Traish and Galoosian (Traish A M, Galoosian A: Androgens modulate endothelial function and endothelial progenitor cells in erectile physiology. Korean J Urol 2013; 54:721-731).
Eisermann et al. reported that the androgen analog R1881 induces VEGF expression in prostate cancer cell lines, thereby probably leading to VEGF-induced angiogenesis (Eisermann K, Broderick C J, Bazarov A, Moazam M M, Fraizer G C: Androgen up-regulates vascular endothelial growth factor expression in prostate cancer cells via an Sp1 binding site. Molecular Cancer 2013, 12:7).
In contrast to that, Chao et al. described anti-angiogenic effects of SR16388, a synthetic steroid with binding properties to the ER alpha and ER beta receptor, (Chao W R, Amin K, Shi Y, Hobbs P, Tanabe M, Tanga M, Jong L, Collins N, Peters R, Laderoute K, Dinh D, Yean D, Hou C, Sato B, Alt C, Sambucetti L.: SR16388: a steroidal antiangiogenic agent with potent inhibitory effect on tumor growth in vivo. Angiogenesis. 2011 March; 14(1):1-16).
The unpredictable effects on angiogenesis are seen also with other well known androgens, which are meanwhile either all banned from the market or withdrawn due to their side effects. Thomas et al. described that Danazol (17α-Ethinyl-17β-hydroxyandrost-4-eno [2,3-d]isoxazol) inhibits certain endothelial cell functions such as proliferation and tube formation but lacks the inhibition of the critical step of invasion into tissue (Thomas G W, Rael L T, Shimonkevitz R, Curtis C G, Bar-Or R, Bar-Or D: Effects of danazol on endothelial cell function and angiogenesis. Fertil Steril. 2007 October; 88 (4 Suppl):1065-70). Due to its androgenic properties (virilization, increase of free testosterone despite inhibition of testosterone synthesis) and its unfavorable profile it was withdrawn from market.
Nandrolone, 17β-Hydroxyestr-4-en-3-on, also a well-known anabolic drug, exerts certain anti-proliferative properties on HUVEC cells (D'Ascenzo S, Millimaggi D, Di Massimo C, SaccaniJotti G, Botrè F, Carta G, Tozzi-Ciancarelli M G, Pavan A, Dolo V.: Detrimental effects of anabolic steroids on human endothelial cells. Toxicol Lett. 2007 Mar. 8; 169 (2):129-36.) However, it is unknown, whether this translates in inhibition of angiogenesis since in an animal model of amyotrophic lateral sclerosis it was observed that nandrolone increases formation of TGF-beta, which is known to stimulate the expression of one of the most potent angiogenic factors, i.e. VEGF (Galbiati M, Onesto E, Zito A, Crippa V, Rusmini P, Mariotti R, Bentivoglio M, Bendotti C, Poletti A. The anabolic/androgenic steroid nandrolone exacerbates gene expression modifications induced by mutant SOD1 in muscles of mouse models of amyotrophic lateral sclerosis. Pharmacol Res. 2012 February; 65(2):221-30). In contrary, Nandrolone reduced VEGF levels in muscles of exercising rats (Paschoal M, de Cassia Marqueti R, Perez S, Selistre-de-Araujo H S. Nandrolone inhibits VEGF mRNA in rat muscle. Int J Sports Med. 2009 November; 30(11):775-8).
Stanazolol (17α-Methyl-5α-androstano[3,2-c]pyrazol-17β-ol) increases the expresssion of TGF beta 1, which is known to increase the production of the most potent angiogenic factor VEGF (Cao Y, Townsend C M, Ko T: Transforming growth factor-beta (TGF-beta) induces vascular endothelial growth factor (VEGF) and plasminogen activator inhibitor-1 (PAI-1) gene expression through Smad3 transcription factor. ACS, 2005 Volume 201, Issue 3, Suppl. 17-18).
Moreover, Thorpe et al. showed that heparin adipic hydrazide- (HAH-) linked cortisol might represent novel angiogenesis inhibitors for the treatment of cancer and other angiogenic diseases (Thorpe P E, Derbyshire E J, Andrade S P, Press N, Knowles P P, King S, Watson G J, Yang Y C, Rao-Bette M.: Heparin-steroid conjugates: new angiogenesis inhibitors with anti-tumor activity in mice. Cancer Res. 1993 Jul. 1; 53(13):3000-7.)
In the light of the various potential target molecules of steroid hormones, e.g. steroid hormone receptors or enzymes, it becomes evident that the outcome of an interaction of a defined cell or tissue with defined steroids is different from gender to gender, from tissue to tissue and the specific pattern of steroid receptors available and active. The specific biological response to steroid hormones is influenced by (i) differences in the expression pattern of e.g. steroid hormone receptors, (ii) the expression of enzymes and (iii) differences in the expression of receptor co-factors (co-activators or co-repressors) modulating the receptor response and (iv) the presence of steroids in the cell culture, organ or tissue. Prediction of a biological response towards a natural steroid or synthetic analogue appears difficult; based on the available literature the skilled person may even predict that testosterone like compounds may induce angiogenesis.
There is a need, and thus it is an objective of the present invention, to provide an effective angiogenesis inhibitor, that is able to inhibit endothelial and/or smooth muscle cell proliferation and/or migration and/or to reduce the synthesis or expression of VEGF and/or of VEGFR, thus inhibiting neovascularization in diseases involving excessive regenerative processes, i.e. processes which occur in various diseases.
These objectives as well as others, which will become apparent from the following description of the present invention, are attained by the subject-matter of the independent claims. Some of the preferred embodiments of the present invention are defined by the subject matter of the dependent claims.